JP2000002101A - Valve system of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a stability of valve behavior in a higher speed rotation area while improving durability, and to stabilize the behavior at seating of a valve so as to avoid a bouncing phenomenon, when a cam profile is applied on an intake cam nose and/or an exhaust cam nose. SOLUTION: This valve system is provided with a cam shaft having at least an exhaust cam profile or intake cam profile. The profile is set such that an absolute value of a acceleration coefficient near a maximum valve lift becomes smaller than an absolute value of an acceleration coefficient in a valve lift region adjacent to an advance angle side and an delay angle side, or a radius of curvature near the maximum valve lift becomes larger than a radius of curvature radius at the valve lift region adjacent to the advance angle side and the delay angle side, and a relation of αup>αdn is established when maximum values of acceleration coefficients in regions where a valve lift increases (up section) and decreases (down section) are αup and αdn, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve train for opening and closing an exhaust valve and an intake valve of a four-stroke engine. More specifically, the present invention can improve durability and operation stability and reduce bouncing phenomena at the time of sitting. It relates to the improvement of the cam profile that can be avoided.

[0002]

2. Description of the Related Art A valve train of a four-stroke engine is for opening and closing an exhaust valve and an intake valve in synchronism with rotation of a crankshaft through a lifter, a rocker arm and the like by an exhaust cam nose and an intake cam nose.

A conventional cam nose of a camshaft is, for example, shown in FIG.
2, a camshaft rotation angle-one-valve lift (head) curve y, a velocity coefficient curve y 'for each camshaft rotation angle when the camshaft rotates at a unit angular velocity, and an acceleration coefficient curve y''
Is generally provided with a cam profile having

The cam nose of the camshaft comprises a base circle portion and a lift portion for actually opening and closing the valve, and the base circle portion is set so as to form a circle having a constant radius Ro centered on the cam shaft center. Have been. On the other hand, the lift section gradually increases the valve litov near the start of opening of the ramp section and the valve until the cam starts pushing the valve directly or via the rocker arm, etc., then increases and decreases in a parabolic manner, and closes the valve. The cam profile is set so as to gradually decrease again near the end and after the camshaft rotation angle at which the valve is seated on the valve seat.

Because of the cam profile described above, the conventional lift coefficient curve y 'of the conventional camshaft (the valve lift curve with the camshaft rotation angle as a variable assuming that the camshaft rotates at a unit angular velocity is differentiated to lift Calculated speed in the direction) shows the positive maximum value in the parabolic increase region of the valve lift, inverts from the positive side to the negative side in the maximum lift region, and calculates the negative maximum value in the parabolic decrease region. Show.

An acceleration coefficient curve y '' (obtained by further differentiating the speed coefficient curve y 'with the camshaft rotation angle)
Indicates the maximum value on the positive side near the parabolic increase start area and the decrease end area of the valve lift, and shows the maximum value on the negative side in the maximum lift area in the area between them, and changes gradually and continuously. .

In the case of the conventional camshaft, as can be seen from the acceleration coefficient curve y '', the acceleration coefficient shows a negative maximum value in the maximum lift range. Therefore, the load acting between the cam nose and the lifter or the rocker arm near the maximum lift is reduced, and when the engine speed is increased, the followability of the two becomes poor, and the limit speed cannot be increased.

The radius of curvature of the cam is expressed by the sum of the equivalent cam lift, the acceleration coefficient, and the radius of the base circle portion in the case of the direct acting type. In the conventional cam profile, the acceleration coefficient near the maximum lift is negative. As can be seen from the maximum value on the side, the radius of curvature near the maximum lift is set small.

The load acting on the cam surface is the inertial mass (valve,
Part of valve spring, rocker arm with rocker arm,
(A valve lifter or the like) and acceleration, and the resilience of the valve spring. On the other hand, since the stress on the cam surface can be considered as contact between the cylinder and the plane, the stress is proportional to the square root of the load acting on the cam surface and inversely proportional to the square root of the radius of curvature of the cam.

In the case of the conventional cam profile, in a low-speed or middle-speed rotation region where the rotation speed of the camshaft is low and the influence of acceleration is small, the stress at the maximum lift portion of the cam surface where the spring force of the valve spring becomes the largest is increased. It shows the maximum value when viewed in the entire profile. When such a conventional cam profile is employed in a valve train of an automobile engine in which low-speed and medium-speed rotations are commonly used, the above-mentioned high stress in the maximum lift portion lowers the durability of the entire valve train. It will be.

Accordingly, the present applicant sets the radius of curvature in the maximum lift region larger than the radius of curvature in the adjacent lift region, thereby reducing the negative side acceleration coefficient in the maximum lift region, thereby reducing the vicinity of the maximum lift. The load acting between the cam nose and the lifter or rocker arm is increased, the followability of both is improved, the limit rotational speed can be increased, and the cam surface stress near the maximum lift is reduced to reduce the overall valve gear. We are developing cam profiles that can improve durability.

[0012]

By the way, it is effective to reduce the maximum value of the positive acceleration in the descending section where the valve lift is reduced in order to make the behavior of the valve accurate in the high speed rotation range of the engine. Conceivable. The reason is as follows. That is, since the acceleration is proportional to the inertial force, when the acceleration changes rapidly, the inertial force also changes rapidly. This causes vibration of the camshaft and the valve stem, and also causes surging of the valve spring. As a result, the behavior of the valve at high speed rotation becomes unstable, and a change in the positive acceleration when the valve is seated causes a bounce phenomenon which causes damage to the valve.

According to the present invention, when the cam profile according to the above development is applied to one or both of an intake cam nose and an exhaust cam nose, the behavior of the valve in a high-speed rotation region can be further stabilized and the durability is improved. It is an object of the present invention to provide an engine valve operating device which can stabilize the behavior when the valve is seated and avoid the bounce phenomenon.

[0014]

According to the first aspect of the present invention, the absolute value of the acceleration coefficient near the maximum valve lift is determined by comparing the absolute value of the acceleration coefficient in the valve lift regions adjacent to the advance side and the retard side. A section in which the valve lift is increased or a section in which the valve lift is increased such that the radius of curvature near the maximum valve lift is larger than the radius of curvature in the valve lift area adjacent to the advance side and the retard side. ), And a camshaft having at least one of an exhaust cam profile and an intake cam profile set so that αup> αdn, where αup and αdn are the maximum values of the acceleration coefficient in the decreasing section (downward section), respectively. It is characterized by:

According to a second aspect of the present invention, in the first aspect, the positive acceleration section lengths of the up section and the down section are each θ
When 0up and θ0dn are set, a camshaft having at least one of an exhaust cam profile and an intake cam profile set so that θ0up <θ0dn is provided.

According to a third aspect of the present invention, in the first or second aspect, the lengths of the ascending section and the descending section are each set to θ1u.
When p and θ1dn, a camshaft having at least one of an exhaust cam profile and an intake cam profile set so that θ1up <θ1dn is provided.

According to a fourth aspect of the present invention, in the first aspect, the positive acceleration section lengths of the ascending section and the descending section are each set to θ.
When 0up and θ0dn, the exhaust cam profile is set so that θ0up <θ0dn, and when the section lengths of the ascending section and the descending section are θ1up and θ1dn, respectively, the exhaust cam profile is set so that θ1up <θ1dn. And a camshaft having at least one of an intake cam profile.

[0018]

According to the first aspect of the present invention, the absolute value of the acceleration coefficient near the maximum valve lift is made smaller than the absolute value of the acceleration coefficient in the valve lift regions adjacent to the advance side and the retard side. Or the radius of curvature near the maximum valve lift is larger than the radius of curvature in the valve lift area adjacent to the advance side and the retard side, so the action between the cam nose and the lifter or rocker arm near the maximum valve lift Therefore, it is possible to prevent the following performance from decreasing when the engine speed is increased.

Further, since the radius of curvature near the maximum valve lift is made larger than the radius of curvature in the valve lift areas adjacent to the advance side and the retard side, a decrease in the radius of curvature near the maximum valve lift can be prevented. An increase in surface stress can be prevented. That is, since the stress on the cam surface is inversely proportional to the square root of the radius of curvature, even if the load acting between the cam nose and the lifter or rocker arm does not decrease or rather increases, the increase in the stress on the cam surface can be prevented, A decrease in the durability of the valve device can be prevented.

As described above, a sudden change in acceleration causes a sudden change in inertial force, for example, a bounce phenomenon that causes damage to a valve. Since this bounce phenomenon is a phenomenon at the time of sitting and is greatly affected by the positive acceleration in the descending section where the valve lift decreases, it is considered that it can be avoided by reducing the maximum value of the positive acceleration in this descending section.

According to the first aspect of the present invention, the maximum value αdn of the positive acceleration coefficient in the descending section is made smaller than the maximum value αup of the positive acceleration coefficient in the ascending section. In addition, the bounce phenomenon of the intake valve and the exhaust valve can be avoided.

According to the second aspect of the present invention, the positive acceleration section length θ0dn in the descending section is larger than the positive acceleration section length θ0up in the ascending section.
It is possible to suppress a decrease in the angle area obtained based on the product of the valve opening area and the opening time due to the reduction of dn.

FIGS. 12A, 12B and 12C show a valve lift curve y, a velocity coefficient curve y 'and an acceleration coefficient curve y'', respectively. In the figure, while decreasing αdn, θ
Since 0dn is increased, the area H can be increased, and the maximum value y'Dmax in the speed curve y 'can be increased. Qualitatively, as y'Dmax increases, the maximum value y in the valve lift curve y
max can be increased. If ymax can be increased, the area B (angular area) can be increased, and the intake air amount can be sufficiently secured to improve the engine performance.

According to the third aspect of the present invention, since the section length θ1dn of the down section is longer than the section length θ1up of the up section, the opening angle of the down section can be made larger than the opening angle of the up section. It is possible to suppress a decrease in the angle area obtained based on the product of the valve opening area and the opening time due to the valve speed in the down section being smaller than the up section.

In FIG. 12, the area D can be easily increased by increasing θ1dn, and the area D can be made equal to the area C while αdn is set to αup. Therefore, the angular area of the descending section can be compared with that of the ascending section. As a result, the engine performance can be improved by securing a sufficient intake amount.

According to the fourth aspect of the present invention, the positive acceleration section length θ0dn in the descending section is made larger than the positive acceleration section length θ0up in the ascending section, and the section length θ1d of the descending section is further increased.
n is longer than the section length θ1up of the ascending section,
The angle area can be further increased, and the performance can be improved.

[0027]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIGS. 1 to 7 are views for explaining a valve train of an engine according to a first embodiment of the present invention. 1 is a cross-sectional side view of a SOHC type valve train, FIG. 2 is a cross-sectional side view of a DOHC type valve train, FIG. 3 is a schematic diagram showing a profile of a cam nose, and FIG. 4 is a profile of a cam nose with a radius of curvature. Figures 5 and 5 show the relationship between the camshaft rotation angle and the acceleration coefficient and the valve Litoff, Figure 6 shows the relationship between the camshaft rotation angle and the load between the canonose and lifter, and Figure 7 shows the relationship between the camshaft rotation angle and the stress on the cam surface. FIG. 6 is a characteristic diagram for explaining the relationship with the above.

In FIG. 1, reference numeral 1 denotes a water-cooled, four-cycle, multi-cylinder engine provided with an SOHC type valve train, which is provided on a cylinder case (not shown) made of aluminum alloy and a cylinder body 10 and a cylinder head. 1
1, a head cover 20 is laminated and connected, and a piston 14 is slidably inserted and arranged in a cylinder bore of a cylinder liner 10c pressed into the cylinder body 10, and the piston 14 is connected to a crankshaft in the crankcase by a connecting rod. FIG. 1 is a cross-sectional side view of a valve operating device for one cylinder.

A combustion recess 11a forming a combustion chamber E is formed in the cylinder head 11 on the cylinder body side facing surface. The combustion recess 11a has three intake valve openings 18 and two exhaust valve openings. 15 are arranged and opened along the outer periphery of the combustion chamber E, and the intake valve opening 18 and the exhaust valve opening 15 are led out to the rear wall and the front wall of the cylinder head 11 by the intake port 31 and the exhaust port 32. ing. 10a is a water-cooled jacket formed on the cylinder body 10, and 30b is an electrode of a spark plug.

Each intake valve opening 18 and each exhaust valve opening 15
Is opened and closed by valve heads 25a and 26a of an intake valve 25 and an exhaust valve 26 which are driven forward and backward by a valve train 40. The intake valve 25 and the exhaust valve 26 are disposed so that their valve shafts 25b, 26b protrude into a cam chamber 24 formed by the cylinder head 11 and the head cover 20, and are movable in the axial direction. A valve spring 35 interposed between a retainer 34 mounted on the protruding end and a spring seat of the cylinder head 11
Urged in the closing direction.

The valve gear 40 is provided with one camshaft 36 arranged in the crankshaft direction so as to pass above the substantially center of the combustion chamber E, and on both sides of the camshaft 36 and above. An intake rocker shaft 46 and an exhaust rocker shaft 47 are provided, and three intake rocker arms 43 and two exhaust rocker arms 42 per cylinder are supported by the respective rocker shafts 46 and 47 so as to be swingable.

The camshaft 36 has three intake cam nose 36a and two exhaust cam nose 36b for each cylinder.
A substantially central portion and both end portions of the combustion chamber are rotatably supported by a cam bearing formed on the cylinder head 11 and a bearing cap mounted on the cam bearing.

The intake rocker shaft 46 and the exhaust rocker shaft 47 are fixedly supported by bosses 20a, 20a projecting downward from the inner surface of the head cover 20. Sliding surfaces 43a and 42a are formed at inner ends of the intake rocker arm 43 and the exhaust rocker arm 42 so as to slide on the cam nose 36a and 36b, and valve shafts 25b of the intake valve 25 and the exhaust valve 26 are formed at the outer end. , 26b are screwed in such a manner that the adjusting bolts 48, 49 contacting the upper end surfaces thereof can be adjusted in axial position. Reference numerals 48a and 49a denote lock nuts, and reference numeral 50 denotes a valve gap adjusting cap detachably mounted on the head cover 12.

In FIG. 2, reference numeral 1 denotes a water-cooled four-cycle engine provided with a direct-acting DOHC type valve train 60, and the same reference numerals as those in FIG. 1 denote the same or corresponding parts. The valve gear 60 includes an intake valve 25 and an exhaust valve 26 each having an independent intake camshaft 61 and an exhaust camshaft 62.
a and 36b are driven to open and close via lifters 63a and 63b.

Each of the camshafts 36, 61, 6 shown in FIGS.
The intake cam nose 36a and the exhaust cam nose 36b have a cam profile which is a feature of the present embodiment, and the cam profiles will be described in detail. In the following description, the case of the intake cam nose 36a in the direct acting valve train shown in FIG. 2 is mainly described, but the same applies to the exhaust cam nose 36b. Also, the intake cam nose 36a and the exhaust cam nose 36b in the valve train of FIG.
The same applies to.

FIGS. 3 and 4 are views for explaining the cam profiles of the intake cam nose 36a and the exhaust cam nose 36b which rotate counterclockwise, and show states at the same timing. In the figure, TDCin is the top dead center in the exhaust / suction stroke, BDCin is the bottom dead center in the suction / compression stroke, TDCex is the top dead center in the compression / explosion stroke, BDC
ex indicates the bottom dead center in the explosion and exhaust strokes. Θin,
θex is the above TDCin and TD before 1 combustion cycle, respectively.
The camshaft rotation angles γin and γex based on Cin ′ are the camshaft rotation angles from the TDCin and TDCin ′ to the contact points Bin and Bex between the cam nose and the lifter, respectively.
Bexo is the contact point at the time of the maximum lift, Pin is the above contact point Bin
, The center of curvature located on a straight line perpendicular to the sliding contact surface of the lifter 63a, and Rin indicates the radius of curvature of the contact point Bin.

In FIG. 3, the exhaust cam nose is β
The relative position between the exhaust cam nose and the lifter when returned by the angle is shown by moving the lifter while fixing the exhaust cam nose. The lifter at this time is 63b ', and θex' is the l combustion at this time. The camshaft rotation angle based on TDCin 'before the cycle, Bex' is the contact point between the cam nose and the lifter,
γex ′ is the rotation angle of the cam shaft from the contact point Bex ′ between the cam nose and the lifter with reference to TDCin ′ one combustion cycle before, and Pex ′ is the straight line perpendicular to the sliding contact surface of the lifter 63b ′ from the contact point Bex ′. The curvature center located above, Rex ', indicates the radius of curvature of the contact point Bex' portion.

In FIG. 3, a virtual TDCin line fixed to the cam profile is a virtual TDCin line fixed to the cam profile when the piston is located at the top dead center of the exhaust / suction stroke when this line coincides with the axis of the lifter 63a. The TDCex line is a line in which the piston is located at the top dead center of the compression / explosion stroke when this line coincides with the axis of the exhaust lifter 63b. In the illustrated state, the intake cam nose 36a rotates the TDCin line by θin from the top dead center position of the exhaust / intake stroke in the direction of the arrow (the direction of rotation of the camshaft), and the exhaust cam nose 36b detects the TDCin ′ one combustion cycle before. This indicates that the reference has been rotated by θex (= θin + 360 °) as a reference.

The intake cam nose 36a includes a base circular portion 70a that does not perform a valve lift function, and a lift portion 70b that includes a ramp portion and a portion that actually lifts the valve. The exhaust cam nose 36b similarly has a base circular portion 71a. And a lift 71b. The base circle portions 70a, 7
1a is an arc having a radius Ro centered on the cam shaft center C, and the radii of curvature of the lift portions 70b, 71b are determined according to the cam shaft rotation angles θin, θex (or γin, γex) in FIG.
It is set as shown in

In FIG. 4, the solid and broken lines represent the radii of curvature of the exhaust cam nose 36b and the intake cam nose 36a, respectively, using the camshaft rotation angle θ and the crankshaft rotation angle Q as parameters. As can be seen from the figure, the base circle 7
The portions 0a and 71a have a constant radius Ro, and no lift action of the valve occurs.

On the other hand, regarding the radii of curvature of the lift portions 70b, 71b, the vicinity a near the start of opening of the valve and the vicinity b near the end of the closing
Is set to the maximum value, so the lift amount increases gradually near the start of valve opening or near the end of valve closing,
Or decrease. Note that a <b is set. In part c between the vicinity of the opening start and the vicinity of the closing end,
The radius of curvature is set to a value smaller than the radius Ro of the base circle portions 70a and 71a, and the valve lift increases in a parabolic manner.

In the case of the conventional cam profile, the radius of curvature in the portion c between the opening start and the closing end is constant or is set to be convex downward in FIG. Are set to be larger by ΔR than the curvature radii Rexo ′ and Rino ′ of the portions adjacent to the advance side and the retard side thereof. That is, the cam profile of the maximum lift portion of the conventional camshaft is sharp, whereas the cam profile of the maximum lift portion of the present embodiment is closer to the radius of the base circle portion than the conventional one.

Here, there is a certain relationship between the above θin and γin, which is determined from the shape of the cam, that is, γin = f1 (θin). Rin is also a function of γin and a function of θin. That is, there is a relationship of Rin = f2 (γin) = f2 (f1 (θin)) = g1 (θin). Note that g1 (θin) means data indicating the radius of curvature shown in FIG. Therefore, Rin = g1 shown in FIG.
Given the data of (θin), Rin = f2 (γin),
And γin = f1 (θin), and thus the shape of the cam nose is determined. That is, when the distance between the camshaft center C and the contact point Bin is Zin, and the distance between the camshaft center C and the lifter in the normal to the lifter lowered from the camshaft center C is yin, the radius of curvature Rin ( Once γin) is determined, Zin (γin) that determines the geometric cam profile and yin (θin) that determines the valve lift amount with respect to the camshaft rotation angle when the intake cam is rotated at a constant camshaft rotation angular velocity are determined. . The distance yin between the cam shaft center C and the lifter is a cam lift curve in the intake cam nose referred to in the present application. The same applies to the exhaust cam nose.

FIG. 5 shows a cam lift curve y (mm) and an acceleration coefficient curve y '' with respect to a change in the camshaft rotation angle (θ).
= D ² f (θ) / dθ ² (mm / rad ² ). In the cam nose cam profile of the camshaft of the first embodiment, the maximum value αdn of the acceleration coefficient during the descending period in which the valve lift y decreases is smaller than the maximum value αup of the acceleration coefficient in the ascending period in which the valve lift y increases. As described above, the absolute value α of the acceleration coefficient near the maximum valve lift is the absolute value α ′ of the acceleration coefficient in the valve lift regions adjacent to the advance side and the retard side.
It is set to be smaller by Δα. In addition,
In the present embodiment, the positive acceleration section length θ0dn indicating the acceleration period of the camshaft rotation in the descending section is set to be the same as the positive acceleration section length θ0up indicating the acceleration period of the camshaft rotation in the ascending section. Θ0dn is increased by θ0up as in the second embodiment.
It may be set larger.

FIG. 6 shows the load acting between the cam nose and the lifter using the camshaft rotation angle as a parameter. The load acting between the cam nose and the lifter is
The load generated by the valve spring and the inertial force [a product obtained by multiplying the inertial mass consisting of the valve, lifter, and part of the valve spring by acceleration. Near the maximum lift, the acceleration coefficient is negative, and the inertial force is negative. The acceleration is the acceleration coefficient y ″ (mm / rad ² ) in FIG.
Multiplied by the square of the actual camshaft angular velocity (for example, ωrad / sec), that is, y ″ × ω ² (m / sec ² ). ]]. In the case of the cam profile of the present embodiment, as can be seen from FIG. 5, since the negative acceleration coefficient near the maximum lift is small, the load F between the cam nose and the lifter near the maximum lift is smaller than the conventional load. It increases by ΔF as compared with the load F ′. As a result, the followability of the lifter to the cam nose is improved, and the lifter operates stably up to higher speeds, thereby increasing the limit rotational speed.

In the present embodiment, the maximum value αdn of the acceleration coefficient in the down section is smaller than the maximum value αup of the acceleration coefficient in the up section. Bounce phenomena greatly affected by positive acceleration can be suppressed, and the behavior at the time of sitting can be stabilized.

As shown by e in FIG. 6, the load between the cam nose and the lifter in the down section is smaller than the load in the up section. Especially on the exhaust valve side, when the exhaust valve is open, heat is not transmitted to the valve seat and heat easily accumulates in the exhaust valve.Therefore, from the umbrella portion of the exhaust valve to the contact portion with the cam nose of the lifter through the valve shaft The amount of heat transmitted is greater on the closed side of the exhaust valve than on the opening of the exhaust valve. In other words, a large load between the cam nose and the lifter acts when the temperature on the closed side of the exhaust valve is higher at a middle speed and a high speed rotation, and the cam nose and the lifter are each easily worn. Since the load between the lifters is reduced and the contact surface pressure is reduced, wear can be prevented.

FIG. 7 shows the stress acting on the cam surface of the cam nose using the camshaft rotation angle as a parameter. As can be seen from the Hertz stress equation, the stress on the cam surface is proportional to the load acting between the cam nose and the lifter and inversely proportional to the square root of the radius of curvature of the cam. In the cam profile of the present embodiment, the radius of curvature near the maximum lift is set large as described above, so that the cam surface stress becomes σ, and the stress is reduced by Δσ from the conventional cam surface stress σ ′.

As shown by f in the figure, the cam surface stress in the down section is smaller than the load in the up section. Particularly on the exhaust valve side, the temperature on the closed side of the exhaust valve is higher as described above, but since the cam surface stress can be reduced, fatigue damage from the maximum contact stress portion of Hertz on the cam surface can be prevented. .

Since the inertia force is proportional to the square of the camshaft rotation speed, the inertia force is relatively small with respect to the valve spring load in a low speed and a medium speed rotation range. Generally, the stress of the lift portion shows a maximum value. Accordingly, in the case of an automobile engine in which low-speed and medium-speed rotations are commonly used, the high stress in the maximum lift region lowers the durability of the entire valve train. In the present embodiment, as described above, the cam surface stress near the maximum lift is reduced by Δσ from the conventional one, and the cam surface stress in the down section is reduced, so that the durability of the camshaft and, consequently, the entire valve train is improved. Can be improved.

FIG. 8 is a characteristic diagram showing a relationship between a camshaft rotation angle, a valve lift, and an acceleration coefficient curve for explaining a second embodiment according to the second aspect of the present invention. In the second embodiment, in FIG. 5, when the positive acceleration section lengths of the ascending section and the descending section are denoted by θ0up and θ0dn, respectively,
The cam profile of the cam nose is set so that <θ0dn.

In the second embodiment, the positive acceleration section length θ0dn in the down section is replaced by the positive acceleration section length θ0 in the up section.
Since it is larger than 0up, it is possible to suppress a decrease in the angular area obtained based on the product of the valve opening area and the opening time due to the decrease in the maximum acceleration αdn in the down section.

That is, FIGS. 11A, 11B and 11C show a valve lift curve y, a velocity coefficient curve y 'and an acceleration coefficient curve y'', respectively. In the figure, while αdn is made smaller than αup, θ0dn is made larger than θ0up, the area H
Can be increased, and the maximum value y'Dmax in the speed curve y 'can be increased. Qualitatively, the larger the value y'Dmax, the larger the maximum value ymax in the valve lift curve y. If ymax can be increased, the area B (angular area) can be increased, and the intake air amount can be sufficiently secured to improve the engine performance.

FIG. 9 is a characteristic diagram showing the relationship between the camshaft rotation angle, the valve lift and the acceleration coefficient curve in the third embodiment according to the third aspect of the present invention. In the third embodiment, when the maximum acceleration coefficient αdn of the descending section is larger than the maximum acceleration coefficient αup of the ascending section and the section lengths of the ascending section and the descending section are θ1up and θ1dn, respectively, θ1up <θ
The cam profile is set to 1dn.

According to the third embodiment, since the section length θ1dn of the descending section is longer than the section length θ1up of the ascending section, the opening angle of the descending section may be larger than the opening angle of the ascending section. By setting the maximum acceleration αdn in the down section to be smaller than that in the ascending section, it is possible to prevent the angular area from being reduced.

FIG. 10 shows a fourth embodiment of the present invention.
FIG. 4 is a characteristic diagram illustrating a relationship between a camshaft rotation angle, a valve lift, and an acceleration coefficient curve according to the embodiment. In the fourth embodiment, the maximum acceleration coefficient αdn in the descending section is set to be smaller than the maximum acceleration coefficient αup in the ascending section, while the positive acceleration period length θ0dn of the descending section is increased.
The cam profile of the cam nose is set so as to be larger than 0up and the section length θ1dn of the down section is larger than the section length θ1up of the up section.

As described above, in the fourth embodiment, the two
In the third embodiment, the positive acceleration section length of the down section,
The intake air volume can be more reliably increased and the engine performance can be improved as compared with the case where the lengths of the descending sections are individually set larger than those of the ascending sections.

[Brief description of the drawings]

FIG. 1 is a SOHC according to a first embodiment of the present invention;
FIG. 2 is a cross-sectional side view of a valve train portion of a type engine.

FIG. 2 is a sectional side view of a valve operating device of a DOHC engine to which the device of the first embodiment is applied.

FIG. 3 is a view schematically showing a cam nose of a cam shaft of the first embodiment device.

FIG. 4 is a characteristic diagram showing a cam profile of a cam nose of the device of the first embodiment by a radius of curvature.

FIG. 5 is a characteristic diagram showing a relationship between a camshaft rotation angle and an acceleration coefficient in the first embodiment device.

FIG. 6 is a graph showing a camshaft rotation angle and a cam nose-lifter load characteristic of the first embodiment.

FIG. 7 is a characteristic diagram of a shaft rotation angle and a cam surface stress of the device of the first embodiment.

FIG. 8 is a diagram showing a camshaft rotation angle / acceleration coefficient characteristic according to a third embodiment of the present invention.

FIG. 9 is a characteristic diagram of a camshaft rotation angle and an acceleration coefficient according to a third embodiment of the present invention.

FIG. 10 is a characteristic diagram showing a relationship between a camshaft rotation angle and an acceleration coefficient according to a fourth embodiment of the present invention.

FIG. 11 is a characteristic diagram for explaining the operation and effect of the present invention.

FIG. 12 shows a valve lift curve in a conventional cam profile,
FIG. 4 is a characteristic diagram showing a speed coefficient curve and an acceleration coefficient curve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 25 Intake valve 26 Exhaust valve 36 Camshaft 40, 60 Valve train y Valve lift curve y '' Acceleration coefficient curve αdn Maximum value of acceleration in down section αup Maximum value of acceleration in up section θ0dn Positive acceleration section in down section Length θ0up Length of positive acceleration section in ascending section θ1dn Length of descending section θ1up Length of ascending section

Claims (4)

[Claims] An absolute value of an acceleration coefficient in the vicinity of a maximum valve lift is made smaller than an absolute value of the acceleration coefficient in a valve lift region adjacent to the advance side and the retard side, or in the vicinity of the maximum valve lift. The acceleration coefficient of the section where the valve lift increases (ascending section) and the section where the valve lift decreases (down section) so that the radius of curvature of the valve lift becomes larger than the radius of curvature in the valve lift area adjacent to the advance side and the retard side. Is the maximum value of α
An engine valve operating device comprising a camshaft having at least one of an exhaust cam profile and an intake cam profile set so that αup> αdn when up and αdn. 2. The exhaust cam profile or the intake cam profile set so that θ0up <θ0dn, wherein the positive acceleration section lengths of the ascending section and the descending section are θ0up and θ0dn, respectively. An engine valve gear comprising a camshaft having one end. 3. The method according to claim 1, wherein when the section lengths of the ascending section and the descending section are θ1up and θ1dn, respectively, at least one of the exhaust cam profile and the intake cam profile set so that θ1up <θ1dn is satisfied. A valve train for an engine, comprising a camshaft having the same. 4. The apparatus according to claim 1, wherein when the positive acceleration section lengths of the ascending section and the descending section are set to θ0up and θ0dn, respectively, θ0up <θ0dn is set, and the section of the ascending section and the descending section is set. An engine valve operating device comprising a camshaft having at least one of an exhaust cam profile and an intake cam profile set so that θ1up <θ1dn, where the lengths are θ1up and θ1dn, respectively.